1. Field of the Invention
The present invention relates to a chemical vapor deposition (CVD) apparatus and a method for forming a nitride layer using the same. More particularly, the present invention relates to a plasma enhanced chemical vapor deposition (PECVD) apparatus used for fabricating a semiconductor device and a method of forming a nitride layer using the same.
2. Description of the Related Art
There is a wide range of uses for a nitride layer in the field of semiconductor devices. One use of a nitride layer is as an etching mask in an etching process for forming metal patterns from an aluminum layer or a titanium layer, and as a protection layer for preventing a semiconductor device from being contaminated. Another use of a nitride layer is as an insulator when formed between conductive layers. Still another use of a nitride layer is as an etch-stopping layer to detect an end point in an etching process.
Typically, a nitride layer is formed by a method of PECVD, as disclosed in the prior art. The prior art discloses that a thin film is deposited by introducing a process gas and a carrier gas into a process chamber sustaining a temperature of about 350-450xc2x0 C. and a pressure of about 1-10 Torr. Then, a high frequency voltage of about 50-200 W at a source radio frequency of 13.56 MHz is applied to the process chamber to create a plasma atmosphere therein.
The method disclosed in the prior art has an advantage that device operation characteristics are not deteriorated because the process is performed at low temperature of about 350-450xc2x0 C. However, the method also has many disadvantages, such as high degree of hydrogen content, low film density, weak oxidation resistance and film lifting, which are caused by high thermal stress after the thin film undergoes subsequent heat treatment processes.
FIG. 1 shows a conventional plasma enhanced CVD apparatus. The conventional plasma enhanced CVD apparatus includes a cylinder-type process chamber that comprises an upper chamber 10, a lower chamber 12 and an insulator 14 inserted between the upper chamber 10 and the lower chamber 12.
The upper chamber 10 and the lower chamber 12 serve as an upper electrode and a lower electrode, respectively, so that an electric field may be generated therebetween.
An external end of a gas supply pipe 18 located outside the process chamber connected to a process gas supply source 20, also located outside the process chamber, is externally inserted into the process chamber through a top portion of the upper chamber 10. The other end, an internal end, of the gas supply pipe 18 located inside the process chamber is connected to a gas distributing plate 16.
FIG. 2 depicts a perspective view of a gas distributor in accordance with the conventional PECVD apparatus.
As shown in FIG. 2, the gas distributing plate 16 is a circular disk and has a plurality of gas distributing nozzles 17 at a bottom surface thereof, for facilitating downward ejection of process gases from the nozzles 17 toward a bottom of the lower chamber 12.
As shown in FIG. 1, the conventional plasma enhanced CVD apparatus further includes a rotating shaft 22 externally inserted into the process chamber through the bottom of the lower chamber 12. An external end of the rotating shaft 22 is connected to a rotating driving source (not shown) for being rotated. The driving source is located outside the process chamber. A susceptor 24 formed of AIN is installed inside the process chamber and connected to an internal end of the rotating shaft 22 to support a wafer 26. Further, The susceptor 24 has a heater (not shown) embedded therein to heat the wafer 26 placed thereon to a predetermined temperature and to control an internal temperature of the process chamber.
Further, a pumping pipe 32 is connected to the bottom of the lower chamber 12 to control an internal pressure of the process chamber and a vacuum pump 30 is connected to the pumping pipe 32.
Still further, the lower chamber 12 is connected to a loadlock chamber 28 at side surface thereof, in which the wafer 26 is placed before being loaded to or after being unloaded from the susceptor 24.
FIG. 3 illustrates a block diagram to explain operation of the conventional plasma enhanced CVD apparatus and a method of forming a nitride layer using the same.
First, a protective film such as an oxide layer having a dielectric constant of about 3.8-3.9 or a nitride layer having a dielectric constant of about 7.5 is coated on inner walls of the process chamber during a step S2. Ions in plasma tend to move toward the inner walls of the process chamber due to capacitance of the process chamber walls, so that an initial nitride layer formed at the beginning of a deposition process has low uniformity in thickness. The protective film on the inner walls of the process chamber serves to prevent the initial nitride layer from having a low uniformity in thickness.
The protective film formed of the oxide layer may be formed by supplying a process gas such as nitrogen oxide N2O or nitrogen monoxide NO and a carrier gas of nitrogen N2 to the process chamber and creating a plasma atmosphere in the process chamber.
The protective film formed of the nitride layer may be formed by supplying process gases of silane and ammonia to the process chamber and then adjusting the internal temperature and pressure of the process chamber, and applying a high frequency power to the process chamber to create a plasma atmosphere therein.
Next, during a step S4, a sheet of wafers is loaded onto the susceptor 24 in the process chamber by a moving means such as a robot arm.
The process chamber maintains an internal pressure of about 0.5-0.7 mTorr after activation of the vacuum pump 30, and an internal temperature of about 400xc2x0 C. after activation of the heater embedded under the susceptor 24. The heater also causes the temperature of the wafer 26 on the susceptor 24 to become about 400xc2x0 C.
Next, the susceptor 24 is rotated at a predetermined speed by the rotating shaft 22.
Next, during a step S6, ammonia and silane as process gases are supplied to the process chamber through the process gas supply pipe 18 and the gas distributing plate 16, and electric power of about 500-1000 W is applied to the upper chamber 10 and the lower chamber 12.
During the step S6, the process gases are converted to plasma due to an electric field induced by the electric power applied to the upper chamber 10 and the lower chamber 12, so that a plasma atmosphere is created in the process chamber.
Next, during a step S8, ions in the plasma atmosphere are deposited on the wafer 26, thereby forming a nitride layer on the wafer 26 after a predetermined time delay.
Next, during a step S10, the process gas supply and the electric power supply to the process chamber stop.
Next, during a step S12, the wafer 26 is unloaded from the susceptor 24 and shifted to the loadlock chamber 28 by the moving means of the robot arm.
Next, during a step S14, particles and process gases remaining in the process chamber are forced to be discharged by initiating a vacuum pump 30 and the inner part of the process chamber is cleaned by a cleaning gas of Argon.
Next, the steps S2-S14 are repeated about 25 times, thereby forming a nitride layer on each of 25 wafers on a sheet.
Finally, after the 25 wafers are coated with the nitride layer, the inner part of the process chamber undergoes a plasma etching cleaning process in a step S16, so that the protective film coated on the inner walls and components in the process chamber, as well as byproducts, are removed. As a result, the process chamber is completely cleaned. The plasma etching cleaning process of the step 16 is performed by supplying a gas of nitrogen trifluoride NF3 and a carrier gas of Ar to the process chamber and converting the same into plasma.
The conventional plasma enhanced CVD apparatus shown in FIG. 1 has some drawbacks.
First, the plasma formed by the conventional plasma enhanced CVD apparatus has very low intensity. The conventional plasma enhanced CVD apparatus has a cylinder-type upper chamber, allowing the plasma formed in the process chamber to spread throughout the inside of the cylinder-type process chamber. Therefore, the intensity of the plasma decreases.
Also, there is a space in the process chamber between the inner wall of the chamber and the susceptor, where the plasma may also spread, thereby further decreasing the plasma intensity.
Second, a nitride layer formed using the conventional plasma enhanced CVD apparatus has poor quality and characteristics. In the conventional plasma enhanced CVD apparatus, the gas distributing plate ejects the process gases directly downward toward the bottom of the chamber. Since the gases cannot be completely converted into plasma, the gases are deposited on the wafer. Accordingly, non-reactive particles may be deposited on the wafer, thereby lowering the quality of the nitride layer.
Further, the protective films formed on the inner walls of the process chamber have a high dielectric constant (for example, about 3.8-3.9 in case of an oxide layer, about 7.5 in case of a nitride layer), so that capacitance of the inner walls of the process chamber is still high. Therefore, ions in plasma are insufficiently deposited on the wafer, thereby forming a nitride layer with poor uniformity in thickness because ions in plasma move toward the inner walls due to the capacitance thereof.
Still further, the process gases of silane and ammonia are simultaneously supplied to the process chamber. However, the silane gas is occasionally transformed into plasma earlier than the ammonia gas. The advanced reaction causes formation of particles containing polysilicon. These particles are deposited on the wafer, resulting in deterioration of the quality and characteristics of the nitride layer.
Still further, in accordance with the conventional plasma enhanced CVD method, the nitride layer formed at a relatively low temperature of 400xc2x0 C. is easily lifted by high thermal stress caused by subsequent heat treatments. The nitride layer in accordance with the conventional method is further limited by having a high degree of hydrogen content, low film density and weak oxidation resistance.
It is therefore a feature of an embodiment of the present invention to provide a plasma enhanced CVD apparatus capable of forming a nitride layer of high quality by preventing a decrease in plasma intensity during a deposition process and a method of forming a nitride layer using the same.
It is therefore another feature of an embodiment of the present invention to provide a plasma enhanced CVD apparatus capable of preventing non-reactive particles from being formed and deposited on a wafer by completely converting reactive gases to plasma and a method of forming a nitride layer using the same.
It is therefore another feature of an embodiment of the present invention to provide a plasma enhanced CVD apparatus capable of reducing capacitance of inner walls of a process chamber, thereby forming a nitride layer of high quality and a method of forming a nitride layer using the same.
It is therefore still another feature of an embodiment of the present invention to provide a plasma enhanced CVD apparatus capable of forming a nitride layer with a low degree of hydrogen content, high density and strong oxidation resistance, and a method of forming a nitride layer using the same.
According to one aspect of the preset invention, a preferred embodiment of the present invention provides a plasma enahnced CVD apparatus. The apparatus includes a process chamber including an upper chamber with a dome shape, a lower chamber, and an insulator placed between the upper chamber and the lower chamber, a gas distributing ring installed in the process chamber for ejecting a gas in an upward direction inside the process chamber, a susceptor installed below the gas distributing ring for supporting a wafer thereon, and having a heater for controlling a temperature of the wafer and an internal temperature of the process chamber, a plasma compensation ring installed at an upper part of side walls of the susceptor, a vacuum pump connected to the process chamber, and an electric power source connected to the upper chamber and the lower chamber.
Preferably, the gas distributing ring has a plurality of nozzles at inner walls thereof, wherein each of the plurality of nozzles is upwardly sloped with an inclination of, for example, 30-60 degrees, thereby allowing upward distribution of a gas. The gas distributing ring and/or the plasma compensation ring may be made of stainless steel.
The plasma enhanced CVD apparatus may further include a loadlock chamber connected to the process chamber.
The susceptor is preferably coated with Al2O3, so that the susceptor is not etched by nitrogen trifluoride plasma during a plasma etching cleaning process.
According to another aspect of the preset invention, a preferred embodiment of the present invention provides a method of forming a nitride layer using a plasma enhanced CVD apparatus. The method includes loading a wafer onto a susceptor, supplying a first reactive gas containing nitrogen N2 to a process chamber, leaving the wafer intact for a first delay time, forming a basic layer on the water by converting the first reactive gas into plasma which is created by applying electric power to the process chamber, leaving the wafer intact for a second delay time, forming a nitride layer on the wafer having the basic layer thereon by supplying a second reactive gas to the process chamber and converting the second reactive gas into plasma, leaving the wafer intact for a third delay time, stopping the supply of the first and second reactive gases to the process chamber, leaving the wafer intact for a fourth delay time, stopping applying the electric power, and unloading the wafer from the susceptor.
The wafer may be loaded and unloaded through a loadlock chamber connected to the process chamber so that the wafer is not exposed to air, thereby preventing oxidation of the wafer.
Ammonia and silane may be used as the first reactive gas and the second reactive gas, respectively.
Forming the nitride layer is preferably performed in the process chamber having an internal temperature of 580-670xc2x0 C., an internal pressure of 0.5-0.7 mTorr, and an electric power applied thereto of 100-700 W.
A protective film may be formed on inner walls of the process chamber before loading the wafer, the protective film preferably being formed of at least two layers (i.e. an oxide layer and a nitride layer), each of which has a dielectric constant different from the others. For example, an oxide layer may be formed on the inner walls of the process chamber, and a nitride layer may be formed on the oxide layer.
The oxide layer as the protective film may be formed by supplying nitrogen oxygen gas N2O or NO to the process chamber and converting the same into plasma. The nitride layer as the protective film may formed by introducing ammonia gas and silane gas into the process chamber and converting the same gases into plasma.
After unloading the wafer, the process chamber may be vacuumed to compulsorily exhaust a gas remaining in the process chamber and a cleaning gas may be supplied to the process chamber.
After unloading the wafer, plasma etching cleaning to clean inner walls of the process chamber and components installed in the process chamber may be performed. The plasma etching cleaning is preferably performed by supplying nitrogen trifluoride gas to the process chamber and converting the same gas into plasma.
These and other aspects, features, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments, which is to be read in conjunction with the accompanying drawings.